1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. For example, it relates to an apparatus that transmits deflection data by optical transmission in electron beam writing.
2. Description of Related Art
The microlithography technique which advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. In order to form a desired circuit pattern on semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high precision is needed. Thus, the electron beam writing technique, which intrinsically has excellent resolution, is used for producing such a highly precise master pattern.
FIG. 7 is a schematic diagram explaining operations of a variable-shaped electron beam (EB) writing apparatus. As shown in the figure, the variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular, such as a rectangular, opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture plate 420, and thereby to irradiate a target workpiece or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g. X direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target workpiece 340 on the stage continuously moving in the X direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture plate 410 and the variable-shape opening 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) method. (For example, refer to Japanese Unexamined Patent Publication No. 2007-043083.)
In the electron beam writing, writing is performed per subfield (SF) which is obtained by dividing the writing region of the substrate into meshes. Since the number of SFs increases with the recent miniaturization of patterns, further improvement is required in speed and precision of processing deflection data concerning deflection to SF. For example, when transmitting a deflection signal from a control circuit by optical transmission, there occurs a communication delay. On the other hand, when irradiating with an electron beam an SF in the mask substrate on the stage which is moving, tracking processing needs to be performed in accordance with the movement of the stage, and thereby it needs to perform deflection to the tracked position. When the writing processing in one SF has been completed, tracking of the next SF position is started. Therefore, if there is a communication delay, writing processing for the next SF will be delayed, thereby causing an increase in the writing time, which degrades the throughput of the writing apparatus.